\\middle

[Uwe Stöhr]

> it is necessary to use \middle so that the middle vertical bar will be
> of appropriate size
> Would it be possible to make LyX understand the \middle code and
> display the vertical bar correctly?

This can be implemented, see
http://www.lyx.org/trac/ticket/1632

eTeX is now actually part of every LaTeX distribution, so we can indeed 
start implement \middle.

regards Uwe